Sinusitis is an inflammation of the paranasal sinuses Figure 01. The paranasal sinuses are air-filled cavities in the facial bones that open into the nasal passage through tiny holes called ostia. Sinusitis occurs when the sinuses become inflamed and the ostia become blocked. In acute uncomplicated sinusitis, symptoms last less than one month, and may be treated by a generalist physician. Chronic sinusitis, defined as sinusitis of at least three months’ duration, may require the care of an ear, nose, and throat (ENT) specialist. Most doctors believe that chronic sinusitis is a result of a series of past infections rather than a single persistent infection.
Figure 01. Paranasal Sinuses
Sinusitis is usually caused by a defect in the muco-ciliary blanket that interferes with normal sinus drainage. Mucus-producing cells and tiny hairs called cilia line the sinuses, and together are called the muco-ciliary blanket. Mucus traps bacteria and other contaminants that enter the sinuses, and then the hair-like cilia sweep them away with a rhythmic, beating motion. Defects in this system can lead to a buildup of mucus and a subsequent sinus infection.
Blocked ostia can also lead to a sinus infection. Sinusitis can result when the ostia are blocked, and the air within the sinuses is absorbed into the bloodstream. The negative pressure created by the blocked ostia draws air and fluid into the sinuses, producing a microbial breeding ground. White blood cells will then invade the sinuses to fight infection, further increasing the pressure within these openings.
A viral infection can lead to sinusitis. A viral infection of the upper respiratory tract, such as a common cold, may lead to sinusitis by interfering with normal mucus flow, or by causing the nasal passages to swell, blocking the ostia.
Bacteria cause nearly all cases of acute sinusitis. While the organism responsible for sinusitis varies depending on which sinuses are affected, Streptococcus pneumoniae and Haemophilus influenza are the most common causative agents in a community setting.
When a person develops sinusitis in the hospital, Staphylococcus aureus and gram-negative bacilli are frequently the cause.
A variety of other organisms can also colonize the sinuses of people with weakened immune systems. Fungi such as Candida and Alternaria, the bacteria Pseudomonas and Legionella, atypical mycobacteria, and in some cases parasites, can live and grow in the sinuses of people with impaired immunity.
People with intact immune systems rarely develop fungal sinusitis, a chronic condition. Fungal sinusitis most often occurs in patients with asthma or nasal polyposis, and is usually caused by Aspergillus fungi. In diabetics, a rare but severe fungal infection called mucormycosis can develop.
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